Method of and apparatus for treating filaments



Feb. 26, 1935. P ABEL 1,992,797

METHOD OF AND APPARATUS FOR TREATING FILAMENTS Filed Dec. 31, 1932 [NVENT 0R. WILLIAM F ZABEL BY MMVZM tend to twist and warp out of shape.

machine.

Patented Feb. 26, 1935 PATENT OFFICE I METHOD OF AND APPARATUS 'FORTREAT- ING FILAMENTS William P. Zabel, Cleveland Heights, Ohio, assignorto General ElectricCompany, a corporation of New York ApplicationDecember-31, 1932, Serial No. 649,705

5 Claims.

My invention relates to filaments for electric incandescent lamps andsimilar devices "and to methods of and apparatus for their manufacture.More particularly, my invention relates to coiled metal filaments,especially to those filaments .which are operated athigh temperaturesand ject of my invention is to eliminate these difliculties.

The coiling operations set up strains in both primary and secondarycoils of a coiled coil filament, part of which are released immediatelyupon removal of the coils from the winding Further distortion occurswhen the mandrels are removed from the coils. New strains are set up inbending the coils to form them into desired shapes. These variousstrains are still further released during heat treatment of the coils byordinary methods, flashing of the mounts and lighting of the filaments.in the lamps.

Heretofore, molybdenum mandrels have been generally used for primary'andsecondary coils. Such coils on mandrels are heat treated at 1200- 1600C. in electric furnaces in an atmosphere of hydrogen. The mandrels arethen dissolved in a mixture of acids, which is a slow and tediousprocess having some corrosive and, therefore, damaging efiect on thetungsten filaments. The above temperatures are too lowto effectively setthe tungsten filament and, being applied after the coils have been cutto lengths, a certain amount of distortion occurs in said coils. Anothermethod of applying a higher temperature treatment consists in heatingthe coils on their molybdenum mandrels in an atmosphere of hydrogen bypassing current through the secondary mandrel. However, since molybdenummelts at approximately 2500 C., temperatures cannot be used which evenapproximate the operating temperature of the filaments when they areburned in lamps. Furthermore, it is dangerous to treat the coils onmolybdenum mandrels near the melting point of the molybdenum because ofcontamination of the coils by diffused molybdenum which results inblackening of the lamps. Tungsten coils which are treated by passingcurrent through inserted tungsten mandrels in the presence of hydrogenpermit of using still higher temperatures close to the melting point oftungsten (approximately 3300 C.) without danger of contaminationfrom'the mandrel. Heretofore no way was known of dissolving outor-otherwise removing the primary mandrel when used The obin a coiledcoil filament without also destroying or attacking the filament.

According to my invention the primary coil is wound on a mandrel whichmay be readily dissolved out, preferably a steel mandrel. The secondarycoil is then wound on a mandrel consisting of a refractory metal havinga melting point substantially as high as the metal comprising thefilament. With a standard tungsten filament I prefer to use a tungstenmandrel for said secondary coil. Said secondary coil generally comprisesa series of spaced segments with an extra long space between consecutivegroups of segments, each group constituting a filament. The primary coilis clamped or 'welded to the secondary mandrel thus holding the coiledcoil on the mandrel just as it was coiled. The coil is then heated toapproximately 1100 C. in an atmosphere of hydrogen to remove aconsiderable part of the coiling strains in the primary coil. The nextstep is to remove the primary mandrel, hydrochloric acid being usedpreferably, to dissolve it out if it is of steel, The coiled filaments,mounted on their secondary mandrels are placed in electric terminals andcurrent passed through the assembly or through the mandrel alone in atreating bottle, in the presence of hydrogen, the filaments being heatedaccording to a predetermined schedule to approximately 2800 C. Theclamps or welded bonds are now removed from the ends of the coils, andthe secondary mandrel is withdrawn, leaving the coiled coil filamentsfree from all mandrel, ready to bemounted as they are, or bent to othershapes.

In the drawing, Fig. 1 is-an elevation of a filament on a primarymandrel; Fig. 2 is a partial elevation of the coil of Fig. 1 being woundaround a secondary mandrel; Fig. 3 is an elevation. of series ofsegments of primary coils wound around a, secondary mandrel and afiixedthereto; Fig. 4 is a side elevation in section of heat treatingapparatus; Fig. 5 is a section along the line 5-5 of Fig. 4; and Fig. 6.is a front elevation of a stationary clip of the apparatus.

Referring to Fig. 1, a, tungsten filament wire 10 is coiled about amandrel 11, preferably 'of steel wire. This coil is then wound around asecondary mandrel 12 (Fig. 2), preferably a tungsten wire, leaving asuitable spacing betweensegments 13 (Fig. 3) and an extra long spacebetween the groupof segments 13 and an adjacent group of segments 14.Saidgroup of segments 13 constitutes one filament. Before 55 removingthe assembly from the coiling machine, the starting and finishing endsof the primary coil are clamped to the secondary mandrel 12 by means ofsmall nuts and bolts or other suitable devices. v

The next operation is to clamp, preferably by welding, the primary coilto the secondary mandrel at two points 15-16 (Fig. 3) about a half inchapartin the space between groups of segments 13-14. Since tungstencannot be readily welded to tungsten, the welds 15,-16 are made ofnickel, although other bonding metal could be used which does notdissolve in hydrochloric acid or strong alkalies. The bolts can now beremoved from the extreme ends of the group of filaments and the coiledcoil on mandrels is se-' curely located just as it was coiled. If thetungsten mandrel is small and quite ductile, this 0011 after having beenwelded can then be continuously heated by passing it through an electricfurnace in the presence of hydrogen at a suitable temperature of nearlya white heat (about 1100 C.) toremove a considerable part of the coilingstrains in the primary coil. The individual groups of segments 13-14 canthen be cut apart between the clamped points 15-16. If the tungstenmandrel 12 is heavy and inherently brittle, it' has-been found moreconvenient to first separate the individual groups 13-14 and then heatthem in an electric furnace at approximately 1100 C. in an atmosphere ofhydrogen.

The next step is to remove the steel mandrel 11 from the primary coils.This is done by inserting the coiled coil assemblyin a hydrochloric acidsolution which dissolves out the said steel mandrel 11, leaving thesecondary mandrel 12 intact and the coils still attached by .the welds15-16 in their proper locations. There now remain a number of segmentsof coil 13 wrapped about the tungsten mandrel 12 and attached to it bythe nickel bonds 15-16 at each end with a free length of primary coil 10and tungsten mandrel extending outside said bonds, as shown by fulllines in Fig. 3. The ends of the coil and mandrel assembly are nowclipped into electrical terminals of the apparatus shown in Fig. 4 whichis fully described hereinafter, and current is passed therethrough in atreating bottle in the presence of hydrogen. The current is regulatedaccording to a predetermined schedule to arrive at any desiredtemperature for the assembly. It is desirable to make the schedules assimple as possible, yet obtain the advantages of germinative graingrowth and removaLof strains without appreciable loss of tungsten. Thegrain growth occurs very rapidly (less than thirty seconds) in straightdrawn tungsten wires of small diameter between temperatures ofapproximately 2200 to 2800 C. I haveobtained the desired result byheating filaments of two to five mil diameter in accordance with thefollowing schedule: The

- current is regulated through the mandrel, or the mandrel and coil, soas to raise the temperature from a red heat to 225 0 C. in approximatelyfifteen seconds, then to- 2800 C. in thirty seconds, and down to a redheat again in thirty seconds. The time schedule may be extended forlarger filaments. This treatment is sufficient to reduce strains ofcoiling and other deformations so that they will not later causedistortion of the filament in the lamp.[

' The heat treating apparatus comprises a stationary clip 17 (Figs. 4and 6) having a pair of jaws 18-19 and a movable clip 20 (Fig. 5) hav-'clip 17, while the jaw 19, also preferably made of molybdenum, ismounted on a slide 23 which is slidably mounted in said clip 17. A coverplate 24 is mounted on the front of said clip 17 to retain the slide 23therein. The slide 23 is moved up and down by a lever 25 which isconnected to said slide by a pin 26 and is pivotally mounted on a pin2'7 in the cover plate 24. The jaws 18-19 are normally kept closed'by aspring 28 mounted on theend of the lever 25 and on a pin 29 in the clip17. Said clip 17 is mounted on a tube 30 which is mounted in a verticalsupport plate'3l and insulated therefrom by an insulating tube 32surrounding said clip tube 30. Said clip tube 30 is cooled by a flow ofwater entering through a tube 33 mounted thereon and passing along theannular space between said tube 30 and tained therein by a cover plate36. Said slide 35 is moved up and down by a lever 37 which is connectedto said slide by a pin 38 and is pivotally mounted on a pin '39 in thecover plate 36. A spring 40, mounted on the end of said lever 37 and ona pin 41 mounted in the clip 20, serves to normally keep the jaw 22closed against the jaw- 21. The clip 20 is mounted on a copper tube 42which is slidably mounted on a tube 43. Said tube 43 is mounted in thesupport plate 31 and insulated therefrom by an insulating tube 44surrounding said tube 43. cooled by a flow of water entering through atube 45 mounted thereon and passing along the annular space between saidtube 43 and a tube 46 mountedtherein, then out through said tube 46. Apair of bolts 47, mounted in the clip 20 and in a block 48, pass througha clamp block 49 which is mounted on the clip tube 43. Springs 50.mounted on said bolts 4'7 between the blocks 48 and 49, tend to keep theclip 20 in yielding contact with said block 49, thereby allowing saidclip 20 on the tube- 42 to slide along the clip tube 43 to compensatefor expansion and contraction of the mandrel 12 which is held betweenthe pairs of jaws 21-22 and 18-19 and kept under tension so that itremains straight. By locating the clip block 49 at difierent pointsalong theclip tube 43, diiferent lengths of mandrel may be handled bythe device. Terminal clips 51-52 mounted on the'clip tubes 30-43 areconnected 10 they are enclosed in a treating bottle 53 which is mountedon rollers 54 and moved along horizontal tracks 55 mounted on supports56. The open end of said bottle 53 enters a groove 57 (Fig. 4) in thesupport plate 31 in which is located a rubber tube 58 which iscompressed by the end of said bottle 53 to form a gas tight joint. Saidtube 58 is held in said plate 31 by cover plates 59. A flow of hydrogenis maintained through said bottle 53, entering through a tube 60 .andflowing out through tubes 61-62, said tube 61 being provided with aseries of holes 63 The clip tube 43 is along the bottom thereof. Thebottle 53 is kept cool by a flow of water through a jacket 64surrounding said bottle, the water enteringthrough a tube 65 and flowingout through a tube 66.

After treating the filament 10, the nickel bonds are clipped off theends thereof and the mandrel 12 is withdrawn, leaving the coiled coilfilament free of all mandrel, ready to be mounted as it is or bent toother shapes for use in lamps, particularly in projection lamps orotherhigh wattage lamps. The coils, having been heated on straightmandrels throughout the treatment, are in perfeet axial alignmentwhereas, minus said mandrels the coils would be bent, particularly inthe portions between segments.

.It is of course entirely possible to dispense with the welds l-l6 oneach individual group of filament segments and, instead, merely clampthe series of groups at each end and treat them thus, rather thansingly. Filaments-made according to my method have been found to besubstantially free from warping and twisting throughout the life of thelamps. The heat treating schedule disclosed herein may of course be usedwith equally good results on standard single coil filaments supported onmandrels, as well as on the coiled coil construction. If, as mentionedabove, a series of groups 13-14 are heated at a time, sleeves or coilsof a refractory substance such'as tungsten may he slipped over the endportions of the filaments between groups 13 and 14, thereby dissipatingthe heat therein so that said ends do not reach the high temperatures ofthe coils themselves, thereby leaving said end portions relativelyductile for mounting on the lead-in wires.

What I claim as new and desire to secure by Letters Patent of, theUnited States, is:

11 The method of making metal filaments which comprises winding afilament wire around a primary mandrel which is considerably lessrefractory than said filament, winding the coilv thus formed with itsmandrel around a refractory secondary mandrel, heating the coiled coilstructure thus formed to nearly a white heat to remove a considerablepart of the strains in the primary coil, removing the said primarymandrel, heating the coiled coil on the secondary mandrel toapproximately 2800- C., and then removing said secondary mandrel.

2. The method of making metal filaments which comprises winding afilament wire around a' primary mandrel which is readily solublecompared with saidfilament, winding the coil thus formed with itsmandrel around a refractory secondary mandrel, heating the coiledcoilstructure thus formed to nearlv a white heat to remove aconsiderable part of the strains in the primary coil, dissolving out thesaid primary mandrel, heat ing the coiled coil on the secondary mandrelto approximately 2800' C., and then removing said secondary mandrel. v

3. The method of making metal filaments which comprises winding afilament wire around a steel wire primary mandrel, winding the coil thusformed with. its mandrel around a refractory secondary mandrel, heatingthe coiled coil -structure thus formed to nearly a white heat toremove aconsiderable part of the strains in the primary coil, dissolving out thesaid primary mandrel, heating the coiled coil on the secondary mandrelto approximately 2800 C., and then removing said secondary mandrel.

4. The method of treating coiled tungsten filaments of small diameterwire which comprises heating said filaments in successive steps toapproximately 2200 C., then to. approximately 2800 C. in approximatelythirty seconds to allow germinative grain growth to take place.

5. The method of heat treatingtungsten filaments of small diameter wirewhich comprises heating said filaments in successive steps to a redheat, then to 2250 C. in approximately fifteen seconds, then to 2800 C.in approximately thirty seconds.

WILLIAM P. ZABEL.

